R. L. Thompson

Novel Quantitative Assays for Estimating the Antimicrobial Activity of Fresh Garlic Juice

Novel agar diffusion and broth dilution assays were developed for quantitatively estimating the antimicrobial activity of fresh garlic juice. Bacteria found to be inhibited by garlic juice in agar diffusion assay included two gram-positive and five gram-negative species. Leuconostoc mesenteroides was not inhibited. Escherichia coli B-103 (HB101, with pJH101, ampicillin resistant, 100 microg ml(-1)) was inhibited and chosen as the standard culture for quantitative assays. The agar diffusion assay was based on the slope ratio method, where the slope of dose response for garlic juice was divided by the slope of dose response for methylmethane thiosulfonate (MMTSO2). Juice from fresh garlic varied in activity between 1.76 and 2.31 microg of MMTSO2 per mg of garlic juice. The activity of juice decreased during 11 months of storage of garlic cloves at 5 degrees C from 2.31 to less than 0.1 microg of MMTSO2 per mg of juice. The broth dilution assay also used the E. coli B-103 culture, which permitted selective enumeration of this bacterium when 100 microg ml(-1) of ampicillin was incorporated into the enumerating agar. Selective enumeration was essential since the garlic juice was not sterile and, thus, contained natural flora. Growth of E. coli was unaffected by 0.1%, delayed by 0.25%, and completely inhibited at 0.5 and 2% garlic juice in broth during 24 h of incubation at 37 micro C. The minimum inhibition concentration of garlic juice by broth dilution assay was, thus, estimated to be 0.5%, which is equivalent to 3.46 microg of MMTSO2 per mg of garlic juice by the agar diffusion assay.

CROSSFLOW FILTRATION OF BRINE FROM CUCUMBER FERMENTATION

Due to environmental concerns, pickle companies are considering ways of reclaiming the brine obtained from cucumber fermentation. The removal of microbial cells is crucial in use of the brine in finished pickle products. The effects of transmembrane pressure (41 to 166 kPa), feed flow rate (7.8 to 15.5 L/min), pore size (500,000 NWCO and 0.2 .m), and cell concentration (optical density of 0.171 to 1.170 at 640 nm) on permeate flux during the crossflow filtration of brine obtained from bulk fermentation of cucumber were studied. Results indicate that the microfiltration membranes exhibited a large flux decline during the first 15 min of operation when challenged with the fermentation brine. The net decline in permeate flux increased with transmembrane pressure, flow velocity, pore size, and cell concentration. Filtration through filter pore size of 0.2 .m or smaller effectively removed the microbial cells present in the brine. Only the transmembrane pressure significantly affected the resistance of the cake formed at the filter surface. From the results obtained from the study, it is possible to use microfiltration to filter sediments and microbial cells from brine obtained from cucumber fermentation.